Internet Engineering Task Force (IETF) P. Gutmann
Request for Comments: 6476 University of Auckland
Category: Standards Track January 2012
ISSN: 2070-1721
Using Message Authentication Code (MAC) Encryption
in the Cryptographic Message Syntax (CMS)
Abstract
This document specifies the conventions for using Message
Authentication Code (MAC) encryption with the Cryptographic Message
Syntax (CMS) authenticated-enveloped-data content type. This mirrors
the use of a MAC combined with an encryption algorithm that's already
employed in IPsec, Secure Socket Layer / Transport Layer Security
(SSL/TLS) and Secure SHell (SSH), which is widely supported in
existing crypto libraries and hardware and has been extensively
analysed by the crypto community.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6476.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Gutmann Standards Track [Page 1]RFC 6476 MAC Encryption in CMS January 2012Table of Contents
1. Introduction ....................................................2
1.1. Conventions Used in This Document ..........................2
2. Background ......................................................2
3. CMS Encrypt-and-Authenticate Overview ...........................3
3.1. Rationale ..................................................3
4. CMS Encrypt-and-Authenticate ....................................4
4.1. Encrypt-and-Authenticate Message Processing ................5
4.2. Rationale ..................................................6
4.3. Test Vectors ...............................................8
5. SMIMECapabilities Attribute ....................................12
6. Security Considerations ........................................12
7. IANA Considerations ............................................13
8. Acknowledgements ...............................................14
9. References .....................................................14
9.1. Normative References ......................................14
9.2. Informative References ....................................14
1. Introduction
This document specifies the conventions for using MAC-authenticated
encryption with the Cryptographic Message Syntax (CMS) authenticated-
enveloped-data content type. This mirrors the use of a MAC combined
with an encryption algorithm that's already employed in IPsec, SSL/
TLS and SSH, which is widely supported in existing crypto libraries
and hardware and has been extensively analysed by the crypto
community.
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Background
Integrity-protected encryption is a standard feature of session-
oriented security protocols like [IPsec], [SSH], and [TLS]. Until
recently, however, integrity-protected encryption wasn't available
for message-based security protocols like CMS, although [OpenPGP]
added a form of integrity protection by encrypting a SHA-1 hash of
the message alongside the message contents to provide authenticate-
and-encrypt protection. Usability studies have shown that users
expect encryption to provide integrity protection [Garfinkel],
creating cognitive dissonance problems when the security mechanisms
don't in fact provide this assurance.
Gutmann Standards Track [Page 2]RFC 6476 MAC Encryption in CMS January 2012